- Downgrading back to 3.55 is always possible using the following steps :
- Download the 4.25 downgrader PUP -- 4.25 Downgrader mirror -- 4.25 Downgrader
Size 176MB (184,595,263 bytes) MD5: 49d80e07fc1f5ca1b0840e02e94635db
- Rename the downloaded file to "PS3UPDAT.PUP" and put it on your USB in: "USB\PS3\UPDATE\PS3UPDAT.PUP"
- While on Rogero CFW4.21, go to System Update from XMB and install the 4.25 downgrader CFW.
- After the downgrader CFW installs you'll be on a hybrid CFW3.55 that will still shows ver4.21 from system settings.
- Enable QA flag by following these steps:

1- Download the Rebug QA_Toggle package from here -- toggle_qa.pkg
2- Put the "toggle_qa.pkg" on USB and Install it on the PS3.
3- Run the "Rebug Toggle QA" from XMB, the screen will go Black and you will see HDD Led activity then if all went fine you will hear 2 or 3 Beeps and the PS3 will Restart back to XMB.
4- If you want to make sure QA flag was set, go to "Network Settings" then apply the following key combo (all at the same time):

L1 + L2 + L3 (press left stick) + R1 + R2 + dpad_down

You should see Edy Viewer, Debug Settings, and Install Package Files if done correctly.